1. Field of the Invention
The present invention relates to a method and apparatus for pumping high viscosity fluids. More specifically, the present invention is a method and apparatus for the delivery of high viscosity paint to moving textile material.
2. Discussion of Background
In the screen printing of textiles, double diaphragm air pumps are used to pump paint through an apertured tube into the interior of a rotary screen, whereafter the paint is forced through the screen and onto a continuous moving sheet of textile material.
The double diaphragm pumps used in such applications have an inlet port into which paint is delivered and an outlet port through which paint is expressed. Two opposing chambers are both fitted with an internal diaphragm. These diaphragms are connected to one another by a reciprocating connecting rod which is actuated by a piston. When actuated, the connecting rod moves the diaphragms to alternatively create a negative and positive pressure within the interior of the chambers. A stroke of the piston results in one chamber experiencing a positive pressure, thereby forcing the paint toward the outlet port. During the same stroke, the opposing chamber experiences a negative pressure, and thereby draws paint from the inlet port. In many double diaphragm pumps, a bleed port, positioned within the housing of the pump, enables air generated by the movement of the diaphragms to be freely vented to the atmosphere. In other double diaphragm pumps, the bleed port is eliminated, and the air generated by the diaphragms is routed through the main exhaust port of the air motor and subsequently to the atmosphere.
The paint used to decorate textile materials, often referred to as "color," "dye paste," "dye stuffs," or "chemicals", is comprised of at least one pigment and a carrier. The paints that impart lighter, softer colors normally require a minimum of pigment, and consequently, the resulting paints are lighter and less viscous, i.e., less than 10,000 centipoise. Lately, shifts in tastes and fashions have prompted the textile industry to switch to the darker, deeper colors as demanded by consumers. These richer, darker colors require a greater quantity of pigment, and therefore, the viscosity of the resulting paint is greater. These darker, richer paints can have a viscosity in the range of 10,000 to 35,000 centipoise.
A major problem confronting the textile industry, as well as other industries involved in transporting high viscosity fluids, is the inability of existing double diaphragm pneumatic pumps to efficiently forward high viscosity (&gt;10,000 centipoise) fluids to rotary screen. This inefficiency is a consequence of the speed at which the connecting rod moves back and forth. When a diaphragm "cycle", i.e., the time taken for the connecting rod to fully extend within one chamber of the pump, is too rapid, insufficient time is given to draw a sufficient amount of viscous fluid into the chamber. Thereafter, when subjected to a positive pressure, the fluid within the chamber cavitates. This cavitation prevents fluid flow toward the outlet of the pump, and reduces the amount of fluid flow through the inlet. This results in an unsatisfactory output flow rate.
The textile industry's response to the problem of efficiently pumping high viscosity paints has been to slow down the conveyor which carries the moving textile material. This solution is clearly unsatisfactory, since it increases production costs and invariably increases unit costs.
Therefore, there exists a need for a double diaphragm pump that can draw a sufficient amount of viscous fluid within the interior of the chambers and thereby efficiently pump high viscosity fluids.